Pupils at the highly rated King Edward VI high school for girls in Birmingham. Photograph: Christopher Furlong/Getty Images

Parents are made to feel guilty if they send their child to a private school, but are allowed to hold the moral high ground if they accept a place at a comprehensive and spend their money on expensive cars, a leading headteacher said today.

Andrew Grant, chair of the Headmasters and Headmistresses' Conference, an association of 250 private schools, said British society put moral pressure on parents for choosing to spend their income on their children's education rather than fritter it away on luxuries.

Speaking at the annual conference of the Independent Schools Council (ISC), which represents 1,300 private schools, Grant said: "It irritates me that there are people living in my own city, in £3m houses, driving BMW 7 series and taking three or four holidays a year, who send their children to the local comprehensive … and feel they have the moral high ground. Why aren't they living in a council flat and driving a Trabant or whatever the latest equivalent is?"

Grant, who is headteacher of St Albans school, said private education was being "singled out for this kind of treatment".

"Why is there a moral pressure not to use your disposable income for the education of your children, but to use it quite happily in other ways? Why is it this shibboleth?" he said.

John Tranmer, a headteacher at Froebelian, a prep school in Leeds, said the government treated private schools as a "proxy for undeserved educational or social privilege".

"My own school charges fees of less than £6,000 a year. It costs virtually the same to educate a child in the state sector and yet we are achieving standards which are exceptional," he said.

Meanwhile, the chair of the ISC, Dame Judith Mayhew Jonas, argued that private schools took in pupils "as diverse, if not more so" than comprehensives. Jonas said it was wrong for society to label private schools as "some sort of posh elite".

She said: "If you look at the range of children that are now getting bursaries in independent schools, if you look at the ethnic mix of our schools, [you see that] we have an incredibly diverse range of schools in the independent sector. What we are saying is, it's wrong to characterise us as some sort of posh elite. That's just not born out by the facts."

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